Protective device for electric circuits



May 17 1927. 1,629,332

C. J. AXTELL PROTECTIVE DEVICE FOR ELECTRIC CIRCUITS Filed May 6, 1925 Inventor CLLnCon J. AxteLL HLS Attbrn qy Patented May 17, 1927.

UNITED STATES PATENT OFFICE.

CLINTON J'. AXTELL, OF SCHENECTADY, NEW YORK, ASSIGNOR T0 GENERAL ELEC- TRIO COMPANY, A C-JRPORATION OF NEW YORK. I

PROTECTIVE DEVICE FOR ELECTRIC CIRCUITS.

Application filed. May 6,

This invention relates to protective devices for electric circuits operating on a plurality of voltages and has for its object the provision of automatic means for preventing the application of a higher voltage to the circuit than is desired. More specifically, the invention provides an automatic electroresponsive protective device which responds to changes in voltage and is particularly adapted for use on electric cars designed for operation on railway systems having different sections of the line at different potentials.

When such a car operates on a railway systen'r having certain portions ot the supply line at a relatively low potential, such as, :For example, 600 volts and other portions oi? the supply line at a higher potential such as 1200 volts, the control and lighting circuits of the car ordinarily are designed to be energized only at 600 volt potential. When the car enters a 1200 volt section of the system, the line voltage is reduced to a value suitable for the control and lighting circuits, usually by means of a dynamotor. Thus when the car is operating on a 600 volt section of the line the control and lighting circuits are connected directly to the supply conductor, while on the 1200 volt sections of the line the control and lighting circuits are connected to the supply conductor through the dynamotor. In an equipment of this kind it is imperative that the control and lighting circuits never should be energized at the higher voltage since the lamps and control equipment may be burned out or serious accidents may result.

A protective device arranged in accord ance with my present invention ettectively prevents the occurrence of accidents ot the above character on multi-voltage electric railway lines, as well as in other connections.

In carrying my invention into effect in an eleetroresponsive voltage protective device, the device is provided with a normally closed circuit controlling contact, as well as a separately operable normally opened circuit controlling contact, and the two contacts are connected to jointly control an electric circuit. The normally closed contact is arranged to be electromagnetically opened only when the impressed voltage exceeds a predetermined value, while the normally open contact is arranged to be closed only when the impressed voltage is below the predetermined value. In this way the normally open con- 1925. Serial No. 28,496.

tact prevents energization of the controlled circuit upon the initial application of :1 voltage higher than the predetermined value, while the opening of the normally closed contact prevents energization of the circuit upon a reduction of the excessively high voltage below the value at which the normally open contact is closed. Thus the two contacts cooperate to close the controlled circuit only when the voltage initially impressed upon the circuit is below the predetermined value.

A better understanding of the invention may be had from the "Following description of the accompanying drawing in which the single figure a schematic diagram of a control system for an electric railway car embodying the invention and designed for operation on electric railways having sections of the supply conductor at differing potentials. 7

Referring to the drawing, current is supplied :from the supply line or power conductor L through the trolley T to operate the electric driving motors 10 and 11 of the car. It will be understood that the conductor L carries current at low potential such as 600 volts in one portion and at high potential such as 1200 volts in another portion. Suitable electrically controlled switch mechanism 12, not shown in detail in the drawing, is provided for controlling the operation of the motors 10 and 11 on both the high and low potential sections of the power conductor L responsively to operation of one of the manually operable master controllers 13 or 14. The control circuits governed by the master controllers 13 and 14, as well as the lighting circuits 15 of the car, are designed to be energized only at a low potential such as 600 volts, and hence are incapable of safe ,ly withstanding the voltage of the high potential sections of the supply conductor.

To prevent the application of a higher voltage, the control and lighting circuits are energized from the trolley T under the control of an automatic change-over mechanism comprising, in the preferred form illustrated, the pneumatically operated switch 16, which is suitably biased as by means of the spring 17 to the position in which it is shown and is operable to its other position under the control of the electromagnetic valve mechanism 18. The pneumatic switch 16 in its biased position connects the low potential below the lockout value (650 controland lighting circuits to the trolley T through a suitable voltage reducing device such as the dynamotor 19 illustrated in the drawing. The dynamotor 19-is of the Well known type, having a pair of commutators A and A and a shunt field winding F and a series field winding F The control and lighting circuits are connected to the mid point of the series field winding F so as to be energized at a definite portion of the volt age impressed upon the dynamoloi' circuit as, for example, half of the impressed voltage. Upon operation of the switch 16 to its other position, the control and lighting circuits are connected directly to the trolley T to be energized responsively to the full voltage of the supply line L.

In accordance with my invention the operation of the change-over mechanism is under the control of eleetroresponsive means connected to be energized responsively to the voltage of the trolley T at all times and arranged to respond to predetermined changes in the voltage impressed upon the trolley. In the preferred form shown, the clectrorcsponsive .means comprises 21- normally closed electromagnetic switch 20 and a separately operable normally open electromagnetic switch 21. The normally closed circuit-controlling contact 22 ofthe switch 20 and the normally open circuit-controlling contact 23 of switch 21 are connected in series in the energizing circuit of the operating winding of the electromagnetic valve mechanism 18 so as to jointly control the operation of the valve mechanism. The operating winding 24 of electromagnetic switch 20 and the operating winding 25 of the electromagnetic switch 21' preferably are connected in series to be simultaneously energized responsively to the voltage impressed upon the trolley T. The normally closed switch 20 is designed to be unresponsive to the low potential impressed upon the trolley T when operating upon the 600 volt sections of the supply conductor L and to operate the normally closed contact 22 to the open' position in which it is shown in the drawing only when the trolley T is in contact with the high, or 1200 volt. sections of the line L, and the energizing voltage is above a certain value, for example, 800 volts. The normally open switch 21 is of the well known lockout type and is designed to be electromagnetically held in the open position in which it is shown when the trolley T is energized from the high: or 1200volt, sections of the supply conductorL and the energizing voltage isabove a predetermined value, for exa1npl"e,"G50 volts; Preferably. the normally open switch" 21 is designed' to respond to close its contacts onl when the Voltage of trolley T- is above a predetermined minimum limit, such as, for example. 400 volts, and volts), which preferably is slightly above the voltage of the low potential sections of the supply eonductor L. Inasmuch as the design and construction of lockout switches having the desired characteristics are well known, further description thereof is deemed unnecessary. The normally closed electromagnetic switch 20 is provided with overlapping auxiliary contacts 26 and-2'7 which are arranged respectively to establish a holding circuit for the operating winding 2 through the re sister 28 anddeenergize the operating windings 25 of switch 21 when the switch 20 operated to the open. position. Further-1mm: the arrangement is such that the normally closed switch 20 maintained in the open position when operated thereto until after the voltage impressed upon the roller '1 is reduced somewhat below the minimum value (400 volts) at which the normally open switch 21 responds. If desired, the voltage reducing resistors 29 and '30 may be inserted in the energizing circuits of the electromagnetic switches 20 and 21 and the electromag netic valve mechanism 18 as shown.

The operation of the control system embodying my invention is as follows: \Vith the trolley T entering upon a high, or 1200 volt, section of the supply conductor L, a sulliciently high voltage will be impressed upon the circuit including the operating windings of the electromagnetic switches 20 and 21 to lock the normally open switch 21 in the open position and operate. the normally closed switch 20 to the open position as illustrated in the drawing. Switch 20 is maintained in the open position with operating winding 24 energized through the contact 26 and the resistor 28 while the energizing circuit for the winding 25 of switch 21 is interrupted at the contact 27. Thus the energizing circuit for the electromagnetic valve mechanism 18 is maintained opened at the contact 22, as well as at the COlllliiClJQmllIlCl the valve mechanism and the pneumatic switch 16 remain in the biased position in which they are shown. Consequently, the control and lighting circuits are energized at the desired low voltage which is one-half the voltage impressed upon the dynamotor 19.

Should the car now pass from a high potential section of the supply conductor L to a low potential section. the trolley T will pass over a sectionalizing insulator (not shown) which separates thehigh and low potential sections of the line. This interrupts the holding circuit of the electromagnetic switch 20 and the latter returns to the closed position. When the voltage of the low potential section of the supply conductor L is impressed upon the trolley T, the electromagnetic switch 20 is insnliiciently energized to be operated from the closed position. while the electromagnetic switch 21 is suitably energ'iz'ed to operate from the open positionin which it is shown to the closed position. Closure of switch 21 completes the energizing circuit of the electromagnetic valve mechanism 18 and the latter responds to admit pressure from a suitable source, not shown in the drawing to the pr .ssurca'esponsive operating mechanism of the pneumatic switch 16. The resulting operation of switch 16 disconnects the dynamotor 19 from the trolley T and directly connects the trolley to the control and lighting circuits 0 the car.

Upon again entering a high voltage section of the supply conductor L the energizing circuit of the electromagnetic switch 21 is interrupted at the insulating section of the supply conductor and the contact 23 returns to the open position in accordance with with its bias, The opening of switch 21 opens the energizing circuit of the valve mecha nism 18 and the valve returns to the biased position in which it is shown, thus discon necting the pressure responsive operating mechanism 01 switch 16 from the source of pressure P and permitting the same to exhaust to atmosphere. Spring 17 at once returns the switch 16 to'its biased portion in which it is shown, thereby reconnecting the control and lighting circuits of the car to the trolley T through the dynamotor 19. Upon contact of trolley T with the high voltage section of the supply conductor the normally open switch 21 is again electromagnetically locked in the open position and the electromagnetic switch 20 operated to the open position in the manner previously described.

It the trolley T should run 01f the high potential section of the supply conductor L it will be evident that the electromagnetic switch 20 again will be deenergiz-ed and re turned to the closed position. Should the operator in replacing the trolley T upon the high voltage section of the supply conductor accidentally place the trolley in an incorrect operating relation therewith, the electromagnetic switch 21 again will be electromagnetically locked out until after the electromagnetic switch 20 has operated to the open position and opened the energizing circuit of switch 21 at the lower auxiliary contact 27. Under these conditions manipulation of the trolley T into the proper operating relation with the high potential section of the supply line may result in drawing an are which reduces the effective voltage within the 0pcrating limits of the lockout switch 21 or even below the drop out value of switch 20. However, due to the fact that the drop out voltage of the electromagnetic switch 22 is below the minimum limit at which the switch 21 responds it will be evident that there is no possibility of the valve mechanism 18 being accidentally energized and causing operation of the pneumatic switch 16 to connect the control and lighting circuits of the car to the high potential section of the supply conductor. Upon the proper return of the trolley T into contact with the high voltage section of the supply conductor, switch 21 again is locked out until alter the switch 20 is operated to the open position.

\Vhile I have described the preferred ruibodimeut of my invention in order to me plain the principles thereof, it will be understood'that the invention may be carried out by other means.

WVhat I claim as new and desire to secure by Letters Patent of the United States, is:

1. A protective device for electric circuits operating on a plurality of voltages comprising a normally closed switch and a normally open switch connected to jointly control the electric circuit, and electromagnetic means connected to be energized responsivel to the voltage impressed upon the circuit tor electromagnetically opening said normally closed switch only when the impressed voltage exceeds a predetermined value and electromagnetically closing said normally open switch only when the impressed voltage is below said predetermined value.

2. A protective device for electric circuits operating on av plurality of voltages comprising a normally closed switch and a normally open switch connected in series in the controlled circuit, and electroresponsive means connected to be energized responsivelv to the voltage impressed upon the circuit tor electromagnetically maintaining said normally open switch in the open position and electromagnetically opening said normally closed switch when the impressed voltage exceeds a predetermined value and electromagnetically closing said normally open switch only when the impressed voltage is below a predetermined lower value.

3. A protective device for electric circuits operating on a plurality of voltages comprising a pair of separately operable electroresponsive switches connected to jointly control the electric circuit and having their operating windings connected in series to be simultaneously energized rcsponsively to the voltage impressed on the circuit, one ot said switches being biased to the open position and arranged to be operated to the closed position only when the impressed voltage is between a predetermined minimum and maximum limit. and the other of said switches being biased to the closed position and arranged to be electromagnetically operated to the open position when the impressed voltage exceeds said predetermined maximum limit and elcctromagnetically maintained in the open position until after the impressed voltage is decreased below said predetermined minimum limit.

1. A protective device for electric circuits operating on a plurality of voltages comprising a normally closed electromagnetic switch and a normal open electromagnetic switch connected to jointly control theel'ectric circuit and having ,their operating windings connected to be simultaneously energized re-' sponsively to the voltage impressed on the circuit, the normally open switch being operable 1'esponsi\-'ely to a lower impressed voltage than the normally closed switch, electroresponsive means for preventing operation of the normally open switch responsively to a higher voltage, and means whereby operation of the normally closed switch renders the normally ope-n switch inactive until after the circuit is substantially deenergized.

5. A'protective device for electric circuits operating on a plurality of voltages com prising a normally closed electromagnetic switch and a normally open electromagnetic switch connected to jointly control the electric circuit and having their operating windings connected in series to be simultaneously energized responsively to the voltage impressed on the circuit, the normally open switch being operable responsively to a lower impressed voltage than the normally closed switch, and auxiliary switch mechanism associated with said normally closed switch for establishing a. holding circuit for the operating winding thereof and for interrupting the energizing circuit of said normally open switch.

6. A protective device for electric circuits operating on a plurality of voltages comprising a normally closed electromagnetic switch and a normally open electromagnetic switch connected to jointly control the electric circuit and havingtheir windings connected to be simultaneously energized responsively to the voltage impressed on the circuit,the normally open switch having an operating winding responsive to a lower impressed voltage than the operating winding of the normally closed switch for closing the normallyopen switch and responsive to a higher impressed voltage for electrically locking the switch in the open position, and auxiliary switch mechanism associated with said normally closed switch for establishing a holding circuit therefor upon operation thereof and for deenergizing the windings of said normally open switch.

7. In an electric railway system, the combination with a supply conductor carrying current of low potential in one portion and high potential in another portion, of a low potential circuit, a switch biased to one position for connecting the low potential circuit to the high potential portion of the supply conductor through a voltage reducing device and operable to another position for connecting the low potential circuit directly to the low potential portion of the supply conductor, anelectroresponsive means for automatically operatingthe said switch to the said other position responsively to a change from the high potential portion of said conduc'tor to the low potential portion thereof.

8. In an electric railway system, the combination with a supply conductor carrying current or low potential in one portion and high potential in another portion, of a low potential circuit, a, switch biased to one position for connecting the low potential circuit to the high potential portion of the supply conductor through a voltage reducing device and operable to a second position for connecting the low potential circuit directly to the low potential portion of the supply conductor, electrically controlled power means for operating the switch to said second position, and electroresponsive switch mechanism connected to be energized responsively to the voltage of said supply conductor and including a normally closed electromagnetic switch and a normally open electromagnetic switch connected to jointly control the energizing circuit or said electrically controlled power means and arranged. to close the said energizing circuit only responsively to the voltage of the low potential portion of the supply conductor.

9. In an electric railway system, the combination with a supply conductor carrying current of low potential in one portion and high potential in another portion, of a low potential circuit, a switch biased to one position for connecting the low potential circuit to the high potential portion of the supply c'onductor through a voltage reducing device and operable to a second position for connecting the low potential circuit directly to the low potential portion of the supply conductor, a pressure responsive device for operating the switch to said second position, an electromagnetic valve mechanism for admitting pressure to said device when energized and biased to exhaust pressure from said device, and electroresponsive means energized responsively to the voltage of said supply conductor for controlling the energizing circuit of said valve mechanism comprising a normally. closed electromagnetic switch responsive only to a voltage greater than that of the low potential portion of the supply conductor and a normally open elec: tromagnetic switch responsive to the voltage of the low potential portion of the supply conductor and unresponsive to a higher voltage, said switches having their contacts connected in series in the energizing circuit of said valve mechanism whereby the said ener gizing circuit is closed only responsively to the voltage of the low potential portion of the supply conductor.

10. In an electric railway system, the combination with a supply conductor carryin current of low potential in one portion and high potential in another portion of a low potential circuit, a switch biased to one posit-ion for connecting the low potential circuit to the high potential portion of the supply conductor through a voltage reducing device and operable to a second position for connecting the low potential circuit directly to the low potential portion of the supply conductor, a pressure responsive device for operating the switch to said second position, an electromagnetic valve mechanism for admitting pressure to said devicewhen energized and biased to exhaust pressure from said device, and electroresponsive means energized responsively to the voltage ot said supply conductor for controlling the energizing circuit of said valve mechanism comprising a normally closed electromagnetic sw1tch responslve only to a voltage greater than that of the low potential portion of the supply conductor and a normally open electromagnetic switch responsive to the voltage 01 the low potential portion 01 the supply conductor and unresponsive to a. higher voltage, said switches having their contacts connected to jointly control the energizing circuit-0t the electromagnetic valve mechanism and their operating windings normally connected in series, and auxiliary switch mechanism associated with said normally closed switch for establishing a holding circuit for the operating winding thereof independent of the operating windings of said normally open switch.

In witness whereof, I have hereunto set my hand this 4th day of May, 1925.

CLINTON J. AXTELL. 

